Moulding method and apparatus

ABSTRACT

A method of moulding an article having a relatively small thickness in relation to its dimensions in plan including providing a mould for the article, locating or forming one or more inserts on a mould face which will define a part of the surface of the moulded article, introducing the material to be moulded into the mould, providing attachment means with an irregular surface in contact with the material, maintaining the mould in such an orientation while the material hardens and mechanically bonds to the attachment means, such that the said mould face is inclined to the horizontal at an angle at which the or each insert is retained on the said face against slipping by friction during the hardening of the material, and providing gas-outlet means from an upper part of the mould in the said orientation to allow the escape of gases during the moulding process. The attachment means is treated on one face or provided with knit loops so as to adhere to the material of the article during curing.

The technical background of the present invention is the moulding ofarticles and particularly, but not exclusively the moulding of articleshaving a relatively small thickness in comparison with their dimensionsin plan. Such articles may be generally planar but do not necessarilyhave to be.

The present invention also comprehends a method of moulding an article.The invention is particularly concerned with the moulding of signs andespecially signs in which characters or other indicia are set in asupporting substrate so as to be visible on at least one face thereof.

One of the problems encountered with moulding processes is that bubblesof gas (in particular air) may form and/or become trapped within thematerial during casting or pouring and, if they are allowed to remain,can have a detrimental effect on the finished article. Such bubbles can,of course, escape if the moulding is carried out in an open mould (thatis one in which the upper surface of the material being moulded isfreely open to the atmosphere or, at least, to an atmosphere within themould itself) but, where the upper surface of the moulded articlecontacts the mould or a mould insert, appropriate escape routes must beprovided for any trapped gases.

When the article being moulded has a substantial bulk, outlets in theupper part of the mould can provide adequate venting but, when thearticle being moulded is relatively thin and flat, effective venting ismore difficult to achieve. In particular, small bubbles may be trappedbetween the upper surface of the moulded material and the mould facecausing tiny cavities in this surface in the finished article. Thisproblem is aggravated when the moulded article has a generally flatsurface with inserts or cavities therein which are formed by inserts ormould parts on the bottom face of the mould where gas bubbles may becometrapped during the filling of the mould.

According to one aspect, therefore, the present invention provides amethod of moulding a generally flat article including the steps of:

-   -   providing a mould for the article,    -   locating or forming one or more inserts on a mould face which        will define one surface of the moulded article,    -   introducing the material to be moulded into the mould,    -   providing attachment means with an irregular surface in contact        with the material,    -   maintaining the mould in such an orientation while the material        hardens and mechanically bonds to the attachment means, such        that the said mould face is inclined to the horizontal at an        angle at which the or each said insert is retained on the said        face against slipping by friction, and    -   providing gas-outlet means from an upper part of the mould in        the said orientation whereby to allow the escape of gases during        the moulding process.

Thus, gas bubbles which might otherwise be trapped at the upper surfaceof the flat article are vented by providing for the mould to be tiltedso that even gas in contact with an upper face of the mould will riseautomatically to the uppermost part of the mould where the bubbles willcoalesce and can readily be vented through one or more ducts to theexterior. This, in itself, provides an effective way of moulding a flatarticle. The invention results, in particular, from a realisation thatsuch a flat article can readily be moulded with inserts in a very simpleand economical way if the inserts are simply placed (or formed in situ)on the lower mould face, provided the mould is not tilted to an angle atwhich such inserts would start to slip. The inserts are thus retained inposition by friction, no other retainer means being required.

The mould inserts may be releasable from the moulded article, formingcavities therein, to allow articles having relatively complex inserts tobe formed easily and economically and with the added advantage that theshapes of the inserts may readily be changed to allow a range ofarticles to be moulded without the expense of providing an entirely newmould for each variant. This not only allows signs of a given shape andsize to be produced having different message-defining inserts but alsosigns of different size and shape by making the, or at least one, of theinserts a full mould thickness effectively to define an edge of themould cavity. Alternatively, and in the particular application to whichthe invention is directed, inserts may be retained in the finishedarticle: the retention may be achieved by the particular shaping of theinsert which forms a key with the moulded article and/or by directbonding of the insert and moulding materials and/or by an adhesive layerapplied to the inserts before the filling of the mould with the materialto be moulded and/or by other suitable means. In the preferredapplication of the invention, direct bonding is employed.

The preferred use of the invention, to which reference will be madebelow without thereby departing from the generality of the invention, isin the moulding of underwater signs for which special plastics materialswith anti-fouling properties are required. Such plastics are known inthe art and do not form part of the present invention and will not,therefore, be specified in detail although, in general, it will beappreciated that they need to be waterproof, sufficiently tough anddurable to withstand the battering and abrasion to which they may besubject, particularly in a submarine environment, and must not provide asurface on which underwater organisms, such as algae and shellfish, cancling as these would gradually obscure the signs. To this latter end,such plastics materials have very low friction surfaces and the surfacesmust also be free from asperities.

Preferably, the moulding material is a silicone. The silicone materialmay comprise one or more of RTV 325, M polymer, XE15-4283, T4, TSE 3455,ELM 4541, RTV 3040, PR910/1101, PR110/30, RTV 430, ELM 4514, althoughany other suitable silicone may be used.

In view of the above requirements, it has been found that underwatersigns need to have very smooth surfaces, especially the surfaces bearingthe message, and it is not acceptable for message elements to be appliedto the surface, for example by painting because this results in surfacediscontinuities at which the aggressive attack of the corrosive medium(i.e. seawater) can commence or, more importantly, allows organisms afoothold on which they can build. Thus, the moulding method of theinvention is particularly suitable in that it allows inserts of onematerial, forming the elements of a message, to be moulded into a faceof a body, or sign, so as to be substantially co-extensive with thatsurface when the body has cured, set or hardened.

In practice, the outer surfaces of the inserts must have similarproperties to those of the main body of the sign. For producing signsfor other purposes than submarine use the inserts could be of adifferent nature from the sign body, even as far as surface form isconcerned, as well as being a different colour or being otherwisevisually distinguishable from the body of the sign, for example byhaving a different surface texture.

In view of the properties required for submarine signs it wouldobviously be convenient to use substantially the same materials both forthe body of the sign and for the message inserts (apart from a colourdifference) but because the properties of the material are such that,once it has cured, it does not adhere to other previously cured bodies,even those of the same material it is not possible to pre-form themessage inserts and place them in the mould for the sign body beforecasting the body material around them, nor is it possible to mould thesign body with appropriate cavities and subsequently cast the lattermaterial into them.

It has been found, however, that there is a way by which it is possibleto use anti-fouling plastics for the mould inserts provided they areused in a partially-cured state, in which they have sufficient cohesionto retain their shapes but have not cured, set or hardened fully; insuch a condition they can still bond to the body material as it cures.

Accordingly the invention further provides the steps of pre-moulding theinserts from a plastics material and using the pre-moulded inserts in apartially-cured state as the inserts for the moulding of the finishedflat article, the insert material curing and bonding to the body of thearticle during the curing of the latter.

In the case of a sign which is to display a message made up from severalparts, whether these are characters, pictograms or other indicia, theneach insert constituting part of the message must be placed in aspecific spatial relationship with the other inserts on the mould facebefore the moulding operation. For this purpose, the indicia may bepre-made, separate from each other and from the mould for the sign body,and arranged manually or robotically on the mould face. More preferably,however, they are moulded directly on the mould face by means ofauxiliary mould means that may be removed once the inserts have curedsufficiently to be substantially cohesive. More particularly, theinserts are preferably moulded in a single mould body formed so thatthey are at their correct mutual spacing and steps are taken to ensurethat the body is appropriately located on the mould face so that theinserts are also located in their correct positions on that face in onesimple operation. Conveniently the mould body is a template for theinserts and is placed on the mould face and its apertures filled withthe raw insert material. In the case of the materials used currently forunderwater signs, the raw material may be spread over the template,squeezed into the apertures and the upper surface scraped off but anymethod of application suitable to a particular material involved may beused.

The template used in the method of the invention may be cut by aso-called ‘template cutter’ and, advantageously, this may be controlledby a computer which can be programmed to determine the shape or shapescut in the template so that a range of different messages may be formed.This enables the messages displayed by the signs produced by the methodto be changed very readily, making short production runs an economicpossibility.

It will be understood that the template, when placed on the mould facefor forming the message must display the message in mirror-image forthis to appear the right-way around to a viewer of the completed sign.It will also be appreciated that some indicia, such as a letter ‘R’require an annular cut which would remove a central part of the letter.Bridges may be left to attach the centre to the periphery of the letterbut, conveniently, temporary bridges may be applied to hold the centrein place while the template is transferred to the mould; this may beachieved for example by applying a transfer sheet to substantially thewhole of one surface of the template to keep all such loose pieces inplace during transfer.

In order to ensure that the template remains in its desired location onthe mould face, it is preferably fixed in place by adhesive although itmay be located or fixed by other means. The adhesives used in all stagesmay be releasable adhesives protected by release films when not in use.Such adhesives are well known in the art.

Submarine signs as discussed above are intended for attachment tosubmarine structures, such as oil rig legs, and must, therefore, notonly be capable of displaying a message but must also be attachable tothe structure. It will be appreciated that, once the sign material hascured, it can no longer be attached to a structure by adhesive becauseof its anti-adhesive properties. Holes could be formed so that it can bebolted to a structure but in such a case the bolts could themselves formsites for unwanted organic growth. The method of the invention thereforepreferably includes a step of locating attachment means for attachingthe finished article, or sign, to a support structure, in the mould forthe flat article and moulding the article so that it is firmly attachedto the attachment means when cured.

The attachment means may, for example, include members, such as straps,which project from the edges or rear face of the article when cured but,for simplicity, the attachment means comprise a sheet of material whichis mechanically bonded to the back face of the article during mouldingand which can itself be bonded to fixings or supports once the articleis cured: a sheet of plastics material such as PVC, suitably treated onone face so as to adhere to the material of the article during curing,is preferred. Such a sheet of material may conveniently be placed on orin the mould part which will form the back face of the article beforethe mould is closed.

Preferably the attachment means is flexible.

Preferably the irregular surface of the attachment means comprises amechanically scuffed surface. Alternatively, the irregular surface maycomprise a chemically edged surface, a ribbed surface, an array of shorthairs or bristles, an array of knitted loops, a velour, a loopedVelcro-like surface, or the like.

Preferably the attachment means comprises an impermeable material, suchas a vinyl material. Preferably the vinyl material is poly vinylchloride.

The attachment means may comprise a combination of materials, forexample, the attachment means may comprise nylon or velour-like hooks orloops with a pvc backing or another impervious backing that can beglued.

The mould for the flat article may be closed before or after fillingwith the material to be moulded depending on the nature of thismaterial, the structure of the mould itself and the nature of anyinserts. In use of the preferred material for forming an underwatersign, this has two constituents which must be mixed just beforeintroduction into the mould but can be poured into the mould. Preferablythe mixture is poured through an aperture provided in the mould in anupper position in its moulding orientation, the inlet aperture beingseparate from the vent aperture or apertures. Mixing may be carried outmanually and/or in batches but such methods tend to be time-consumingand wasteful of materials. Hence a mixer/dispenser is preferably usedwhich includes means for metering controlled amounts of the constituentsinto a vessel where they are mixed automatically to a more homogenousstandard than achievable manually and further includes means fordelivering the mixed ingredients to the mould. Such automated equipmentwould even more preferably operate with continuous supplies of theconstituents to the mixing vessel and deliveries to a succession ofmoulds on a production line.

Once a mould is filled and closed, it must be maintained at an angle tothe horizontal to ensure that gas is vented therefrom and is not trappedas tiny bubbles at the upper surface of the moulded material, whetherthis is between the moulded material and a plastics insert or betweenthe moulded material and the mould itself. As it is easier to locate theinserts on a horizontal surface and, indeed, if inserts are moulded onthe mould face by means of a template, this step must be carried out ona horizontal surface, the mould is preferably tilted to the curingposition once the inserts have been located and any auxiliary mouldparts have been removed and more usually, before filling with thematerial to be moulded.

According to another aspect of the invention, there is providedapparatus for moulding a generally flat article, comprising a shallowmould part with a flat mould face which will define an under surface ofthe moulded article, inserts or means for forming inserts for locationon the said mould face, attachment means for mechanical bonding to thematerial, means for closing the mould, means for supporting the closedmould in an orientation in which the said mould face is inclined to thehorizontal at an angle at which the or each insert is retained on thesaid mould face against slipping by friction, and means for venting gasfrom an upper part of the mould in the inclined position of the mould.

The apparatus may include any features described above in relation tothe moulding method of the invention. In particular, it preferablyincludes means for supporting the mould with the flat, insert supportface in a substantially horizontal position for the location or formingof the insert or inserts thereon and for moving the mould to itsinclined position for the curing of the moulded article. Preferably thesupport means comprise a support frame or table pivotable between thesubstantially horizontal and the inclined positions.

Such a frame or table is preferably pivotally mounted on a base so as tobe supported at a convenient working height for pivoting about ahorizontal axis. The mould may be fixed to or incorporated in the frameor table or releasable therefrom and possibly interchangeable with othersuch moulds. Moreover the support frame or table may be pivotable in oneor both senses from the horizontal position and may be fixable orlockable in any position, or in discrete positions, between thehorizontal and a vertical position.

The mould itself preferably comprises two parts, a first, lower partdefining the insert-support face, and a second upper part which closesover, and seals with, the lower part. In a preferred embodiment of theinvention, the mould is vacuum-sealed. This enables the mould to beclosed and sealed very quickly and efficiently while the opening of themould is equally convenient.

One embodiment of the invention will now be more particularly described,by way of example, with reference to the accompanying drawings, inwhich:

FIGS. 1 to 6 show schematically successive steps in the production of asign according to the invention, the dimensions being exaggerated forclarity of illustration;

FIG. 7 is a schematic perspective view of part of equipment usable inthe production of a sign according to the invention;

FIG. 8 is an end elevational view taken in the direction of the arrowVIII of FIG. 7, also showing an upper mould part of the equipment;

FIG. 9 shows a detail of the equipment of FIG. 7 on an enlarged scale;and

FIG. 10 is a diagrammatic plan view of a variant of a mould part of theequipment.

With reference to FIGS. 1 to 6, these show various steps in theproduction of a sign, generally indicated 10 in the final FIG. 6 of theseries, particularly for underwater use.

FIG. 1 is a perspective view showing a step in the production of atemplate 110 (FIG. 2) formed from a sheet 11 backed by a coating ofadhesive 12 and a release lining sheet 13. The outlines 14 of thecharacters, which will subsequently constitute the content of the sign,have been cut in the relative positions they are to occupy in the signbut in mirror image.

The character outlines 14 are cut by a sign cutter (not shown)preferably controlled by a computer such that the information displayedby signs made by the process can readily be changed.

Once the outlines 14 have been cut, the pieces of sheet material 11 awithin the outlines 14 are removed, leaving apertures 14 a, and anadhesive transfer sheet 15 is applied to the upper surface of the sheet11 to hold loose parts surrounded by annular incisions, such as thecentre 11 b of the “O”, in position: this condition is shown in sectionin FIG. 2.

The release lining sheet 13 is next removed before the now-completedtemplate 110 is placed in a first mould part shown at 16 in FIG. 3 forthe forming of the characters. The template 11, as shown, occupies theentirety of a flat base face 17 of the mould 16 surrounded by upstandingperipheral walls 18 but it may occupy only a small area of this surface,with appropriate positioning so that the characters are in a desiredrelationship with the edges of the finished sign.

Once the template is positioned, the various sheet parts 11, 11 b adhereto the first mould part 16 by means of the adhesive coating 12 and thetransfer sheet 15, which also has a releasable adhesive coating, isremoved. This stage is shown in section in FIG. 3: at this stage thebase face 17 of the mould part 16 is horizontal although it could,alternatively be inclined to the horizontal as shown in FIG. 5.

The characters are next formed by the filling of the template apertures14 a with black or other coloured material 19 which has appropriateanti-fouling properties when hardened. The currently-preferred materialis liquid and may be brushed, squeezed or sprayed into the template, orotherwise applied so that it fills the apertures 14 a completely and thetop surface is scraped flat.

The character material 19 is left to cure for a certain amount of time,sufficient to ensure that the characters will not deform either when thetemplate 11 is removed or during the subsequent moulding process,described below, but not so much that they will not bond fully with thematerial subsequently co-moulded over them.

While the character material 19 is curing, a second mould part 20 (shownin the sectional view of FIG. 4 together with the first mould part 16)is prepared by the positioning of a backing sheet 21 on its flat surface22 which is of the same size and shape as the base face 17 of the firstmould part 16; such that the face of the backing sheet 21 not in contactwith the flat surface 22 is provided with Velcro-like knit loops. Thebacking sheet 21 is currently preferably of plastics material, such asPVC, provided with Velcro-like knit loops on at least one surface, whichmay be secured in place by any suitable means depending on the nature ofthe mould part 20. In particular, the sheet 21 is currently secured bypins inserted through it into the mould itself but the use of vacuumclamping is envisaged. Additional backing sheets such as sheet steel arealso envisaged and would be secured appropriately to the backing sheet21.

Once the character material 19 has cured appropriately, the template 11is removed and the second mould part 20 is closed over the first mouldpart 16, which at this stage is still horizontal or substantiallyhorizontal and the mould is sealed. The completed mould 16, 20 is thentilted to the position shown in cross-section in FIG. 5, in which thebase face 17 is inclined to the horizontal. The partially curedcharacters, here indicated 19 a, 19 b must be retained in their correctpredetermined positions on the face 17 by friction and therefore themould must not be tilted to a point at which they start to slip.

The mould cavity is next filled with uncured plastics substrate material24 through an aperture 23 in an upper part of the mould, in the tiltedposition, while air escapes through outlets (not shown), also in theupper part, such that the mould can be filled without any air bubblesbeing trapped. The substrate material 24 is similar to the material 19forming the characters 19 a, 19 b but of a different colour.

Once the mould is filled, the plastics substrate material 24 is allowedto cure at least to the stage at which it is cohesive before the mouldis opened. The materials are selected such that, during the curing ofthe substrate material 24, the latter bonds both to the partly curedcharacter material 19 and to the backing sheet 21. The three parts 19,21 and 24 can thus be handled as a unit when the completed sign 10 isremoved from the mould. The sign 10 is shown in perspective, theright-way up for viewing in FIG. 6, it having been moulded upside-downin the steps described above.

In the completed sign 10, the faces of the characters 19 a, 19 b areflush with the face of the sign itself, there being no asperities onwhich organic growths could take hold. Moreover, when cured, thematerials 19, 24 forming the front face of the sign resist growthadhesion so that the message presented by the characters 19 a, 19 b willremain visible in the position of use in the long term.

With reference to FIGS. 7 to 9 of the drawings, equipment for moulding asign 10 is shown generally indicated 30. Parts of the equipmentequivalent to those shown in FIGS. 1 to 6 are indicated by the samereferences.

The equipment 30 thus includes a first, or lower, mould part 16 having abase, or moulding, face 17. The mould part 16 is in fact constituted bya sheet 31 of aluminium having rectangular section filets 32 of wood orother material secured to the face 17 along one longer and two shortersides thereof to constitute the peripheral wall of the mould; the fourthside is left open.

In view of the thin flexible nature of the aluminium sheet 31, it isreinforced on the back by aluminium or mild steel angle sections 33 thatextend parallel to the longer axis of the sheet 31. The angle sections33 are in turn supported at each end by end-support angle sections 34extending parallel to and beneath the shorter ends of the sheet 31.

Each end support section 34 is pivotally mounted at the upper end of arespective square-section upright 35 of a base frame generally 36 whichsupports the mould part 16 at a suitable height above the floor. Theremaining structure of the base frame 36 will not be described as it isnot relevant to the invention. What is relevant is that the pivot pins37 attaching the mould part 16 to the uprights 35 are coaxial andparallel to the longer axis of the aluminium sheet 31 to enable this topivot about a horizontal axis parallel to this longitudinal axis. Thepivot pins 37 are readily releasable to enable the mould part 16 to bereleased from the base 36.

As best seen in FIG. 9, each end support section 34 of the mould part 16also carries a semi-circular flange 38 which is dependent from it andlies adjacent the outer end face of the respective upright 35. The innerface of each flange 38 carries two projecting stops 39, 40 spaced apartaround its periphery, each for contacting a respective outer side faceof the upright 35; each stop 39 in practice contacts its upright 35 inthe horizontal, or substantially horizontal position, of the sheet 31shown in FIG. 7 to prevent the mould part 16 from pivoting beyond thisposition in one sense while the stops 40 contact the opposite faces ofthe uprights 35 to prevent pivoting in the opposite sense beyond thetilted position shown in FIG. 8.

A further feature of the base frame 36 are turn-clamps generallyindicated 41, one carried on the outer end face of each upright 35adjacent the outer edge of the respective mould flange 38. The clamps 41are of generally known type but, in general, comprise a bolt passingthrough the upright and carrying a clamping plate and turn bar which canbe rotated manually to clamp the adjacent flange 38 between the clampingplate and the upright 35 and thereby clamp the mould part 16 in adesired position against pivoting.

With reference now to FIG. 8 of the drawings, in particular, this showsthe base frame 36 and lower mould part 16 together with an upper mouldpart 20.

The mould part 20 has a similar structure to that of the lower mouldpart 16 in that it is constituted by a sheet 31 a of the same size asthe sheet 31, reinforced on the back by angle sections 33 a. It doesnot, however, have additional angle-section end supports equivalent tothe supports 34, nor filets 32 along three sides. Instead it has one ormore filet pieces 32 a along one of its longer sides which, when the twomould parts are brought together, in use, mates with that side of themould part 16 which does not carry the filet 32.

When the two mould parts 16, 20 are brought together, the filets 32, 32a ensure that the mould faces 17, 22 of the two parts are spaceduniformly apart. Gaps are however left between the fillet pieces 32 aalong one longitudinal edge which is uppermost in the tilted conditionof the mould shown in FIG. 7.

For use of the mould part 20 for the manufacture of a sign as describedabove, the sheet 31 a need not be of aluminium as it does not itselfcontact the material to be moulded: a sheet is placed over it before themoulding step. Instead a cheaper material may be used for the sheet 31a; a plastics coated chipboard edged with softwood is currentlypreferred for reasons indicated below.

In the embodiment shown in FIGS. 7 to 9, the two mould parts are clampedin this condition by clamping bolts (not shown) which pass throughco-operating apertures (not shown) formed in the sheets 31, 31 a and thefilets 32, 32 a.

In an alternative embodiment shown diagrammatically in FIG. 10, whichwill be described briefly below, the two mould parts are vacuum-clampedtogether.

A final feature of the mould part 20 is an inlet duct 43 connected to anaperture (not shown) in its moulding face and which communicates withthe interior of the mould when the two parts are brought together.

In use of the equipment 30, the mould part 16 is first arranged with itsface 17 horizontal while the template described above is used to formcharacters on it and then removed. A suitably-treated sheet (not shown)is then applied to the mould face 22 of the second mould part 20 so asthe overlap the edges and is pinned in place by drawing pins insertedthrough the plastic sheet into the softwood edging strips. The secondmould part 20 is then applied and clamped to the first mould part 16 andthe entire mould is tilted to the position shown in FIG. 8.

The plastics material for forming the body of the sign is mixed andpoured into the mould cavity through the duct 43 very quickly thereafterto avoid the characters curing to too great an extent. Any air in themould escapes through the gaps between the filet pieces 32 a along theupper edge of the mould. The mould may then be left for the plastics tocure before the completed sign is finally released from the mould.

With reference finally to FIG. 10 of the drawings, this shows a variantof the mould part 16. In this embodiment the clamping bolts and theirapertures 45 are replaced by vacuum clamping means. For this purpose thefilets 32 are widened and formed with a continuous channel 46 in theirupper surfaces. The two ends 47 of the channel 46, close to the freeends of the filets 32, are closed but the channel communicates throughan aperture 48 in its base with a vacuum source, not shown.

When the mould constituted by the parts 16 and 20 is closed, the channel46 is evacuated so that atmospheric pressure clamps the two partstogether. This provides a very much quicker method of clamping andreleasing the mould parts than the use of clamping bolts.

EXAMPLE Test of the Bonding Strength

Test samples were prepared sized 100 m×150 mm and tested using a clampto hold the free end of the silicone attached to the hook of themeasuring scales. A further clamp was used to hold the free end of thebacking sheet of the samples. The scales were then attached to a chainblock and the scales tensioned until there was separation of the twomaterials. This initial separation is used as the maximum load. Onceseparation of the silicon from the backing sheet occurred, the chainblock was stopped immediately, and the load left connected to the clampsuntil the downward movement of the scale stabilised. This reading wastaken as the sustained load.

The results of the bonding strength tests are shown below: Load toSustained Test No. Backing Silicone start peel Load 1 PVC Wacker ‘m’ 10kg   8 kg polymer 355Z 2 PVC Wacker ‘m’ 11 kg  8.5 kg polymer 355Z 3Aplix^(RTM) 200 RTV 430 16 kg   15 kg 4 Aplix^(RTM) 200 RTV 430 16 kg  15 kg 5 VELCRO^(RTM) 3607 RTV 430 17 kg 16.5 kg VELOUR 6 VELCRO^(RTM)3607 RTV 430 16 kg 15.5 kg VELOURPVC—Poly vinyl chlorideAplix^(RTM) 200 - commercially available polyamide knit loop material(available from APLIX).Velcro^(RTM) 3607 velour - commercially available vinyl laminate with aknit loop surface.

Samples 1 and 2 comprise a silicone moulding chemically bonded to a PVCbacking sheet. Samples 3 and 4 comprise an RTV 430 moulding compoundmechanically bonded to a vinyl backing. Samples 5 and 6 comprise an RTV430 moulding compound mechanically bonded to Velcro™ velour, that isknit loops provided on a vinyl backing sheet.

As can be seen from the above table, samples 3 to 6 showed superiorbonding strength when compared with samples 1 and 2. The mechanicalbonding of the silicone moulding compound to the knit-loops on thebacking sheet provides improved bond strength properties to the finalmoulded product when compared with the bonding strength properties offinal moulded products relying on a chemical bond between the siliconemoulding product and the backing sheet to provide bond strength.

1-25. (canceled)
 26. A method of moulding an article having a relativelysmall thickness in relation to its dimensions in plan includingproviding a mould for the article, locating or forming one or moreinserts on a mould face which will define a part of the surface of themoulded article, introducing the material to be moulded into the mould,providing attachment means with an irregular surface in contact with thematerial, maintaining the mould in such an orientation while thematerial hardens and mechanically bonds to the attachment means, suchthat the said mould face is inclined to the horizontal at an angle atwhich the or each insert is retained on the said face against slippingby friction during the hardening of the material, and providinggas-outlet means from an upper part of the mould in the said orientationto allow the escape of gases during the moulding process.
 27. A methodaccording to claim 26 wherein the attachment means is a sheet.
 28. Amethod according to claim 26 wherein the attachment means is flexible.29. A method according to claim 26 wherein the irregular surface of theattachment means comprises a mechanically scuffed surface.
 30. A methodaccording to claim 26 wherein the irregular surface of the attachmentmeans comprises a chemically etched surface.
 31. A method according toclaim 26 wherein the irregular surface of the attachment means comprisesa ribbed surface.
 32. A method according to claim 26 wherein theirregular surface of the attachment means comprises an array of shorthairs or bristles.
 33. A method according to claim 26 wherein theattachment means is provided with knit loops.
 34. A method according toclaim 33 wherein the attachment means has a looped Velcro-like surface.35. A method according to claim 33 wherein the attachment means is avelour.
 36. A method according to claim 26 wherein the attachment meanscomprises an impermeable material.
 37. A method according to claim 26wherein the attachment means comprises a vinyl material.
 38. A methodaccording to claim 37 wherein the vinyl material is poly vinyl chloride.39. A method as claimed in claim 26, in which, during the introductionof the material to be moulded, the mould is supported in an orientationin which the said mould face is substantially horizontal and, after theintroduction, is moved to an inclined orientation at an angle at whichthe or each insert is retained on the mould face against slipping byfriction, for the article to set, cure or harden.
 40. A method asclaimed in claim 26, in which at least one insert is retained in thefinished moulded article.
 41. A method as claimed in claim 40, in whichthe said at least one insert to be retained is a partially-cured mouldedarticle which sets, cures or hardens and bonds to the moulding materialas this latter itself sets, cures or hardens.
 42. A method as in claim41, in which a plurality of the said inserts are moulded in a singlemould body so shaped that the inserts have a predetermined spacing andorientation, which is maintained as the inserts are transferred to theirposition on the said mould face.
 43. A method as claimed in claim 41, inwhich the or each insert to be retained is moulded directly on the mouldface by means of subsidiary mould means which are removed when theinsert has cured sufficiently to be at least substantially cohesive. 44.A method as claimed in claim 41, in which the subsidiary mould meanscomprise a template having cut-out portions defining the or each insert,and material for forming the insert is applied to the apertures in thetemplate.
 45. A method as claimed in claim 44, in which the template isplaced in contact with the said mould face and the material for formingthe insert applied thereto by spatula and scraped off level with thesurface of the template.
 46. A method as claimed in claim 42, in which atransfer sheet is applied to a partly cured insert to maintain thecomponent parts thereof in a predetermined relative orientation and/orspacing upon transfer from the said mould body to the said mould face.47. A method as claimed in claim 43, in which the template is cut by acutter controlled by computer means which is programmable to determinethe shape or shapes of the cut-out portions to be changed to formdifferent inserts.
 48. Apparatus for moulding an article having arelatively small thickness in relation to its dimensions in plancomprising a shallow mould part with a flat mould face which will definean under surface of the moulded article, inserts or means for forminginserts for location on the said mould face, attachment means formechanical bonding to the material, means for closing the mould, meansfor supporting the closed mould in an orientation in which the saidmould face is inclined to the horizontal at an angle at which the oreach insert is retained on the said mould face against slipping byfriction, and means for venting gas from an upper part of the mould inthe inclined position of the mould.
 49. A moulded sign for underwateruse having a relatively small thickness in relation to its dimensions inplan comprising a layer of moulded material in a first colour andcontaining at least one pre-moulded insert of a second colour, the signfurther comprising attachment means moulded into the sign, wherein theattachment means has first and second major faces opposite one another,wherein the first major face is moulded in contact with the layer ofmoulded material of the first colour, and the second major face is leftexposed, and wherein the first major face has an irregular surface. 50.A moulded sign according to claim 49 wherein the attachment is a sheet.51. A moulded sign according to claim 49 wherein the attachment means isflexible.
 52. A moulded sign according to claim 49 wherein the irregularsurface of the attachment means comprises a mechanically scuffedsurface.
 53. A moulded sign according to claim 49 wherein the irregularsurface of the attachment means comprises a chemically etched surface.54. A moulded sign according to claim 49 wherein the irregular surfaceof the attachment means comprises a ribbed surface.
 55. A moulded signaccording to claim 49 wherein the irregular surface of the attachmentmeans comprises an array of short hairs or bristles.
 56. A moulded signaccording to claim 49 wherein the attachment means is provided with knitloops.
 57. A moulded sign according to claim 49 wherein the attachmentmeans has a looped Velcro-like surface.
 58. A moulded sign according toclaim 49 wherein the attachment means is a velour.
 59. A moulded signaccording to claim 49 wherein the attachment means comprises animpermeable material.
 60. A moulded sign according to claim 49 whereinthe attachment means comprises a vinyl material.
 61. A moulded signaccording to claim 60 wherein the vinyl material is poly vinyl chloride.62. A moulded sign as claimed in claim 49, in which the said at leastone insert is partially-cured.
 63. A moulded sign as claimed in claim49, in which the said at least one insert is bonded to the layer ofmoulded material of the first colour.
 64. A moulded sign as claimed inclaim 49 comprising a plurality of the said inserts.
 65. A moulded signas claimed in claim 64, in which the plurality of inserts have apredetermined spacing and orientation.
 66. A moulded sign as claimed inclaim 49, in which the moulded material is silicone.
 67. A moulded signas claimed in claim 49, in which the moulded material has very lowfriction surfaces and anti-fouling properties.
 68. A moulded sign asclaimed in claim 49, in which the second major face is left exposed forattachment to another object.